The present invention relates to a catalyst for polyester preparation, a process for preparing a polyester using the catalyst, and a polyester prepared by the use of the catalyst. More particularly, the invention relates to a catalyst for polyester preparation capable of polycondensing a dicarboxylic acid and a diol with excellent catalytic activity, a process for preparing a polyester using the catalyst, and a specific polyester prepared by the use of the catalyst.
Polyesters such as polyethylene terephthalate are excellent in mechanical strength, heat resistance, transparency and gas barrier properties, and they have been favorably used as materials of containers to be filled with beverages such as juices, soft drinks and carbonated beverages and materials of films, sheets, fibers and the like.
Such polyesters are conventionally prepared using a dicarboxylic acid such as terephthalic acid and a diol such as ethylene glycol as starting materials. More specifically, a low condensate (ester low polymer) is first formed by esterification reaction of a dicarboxylic acid with a diol, and then the low condensate is subjected to deglycolation reaction (liquid phase polycondensation) to give a high-molecular weight product. In some cases, solid phase polycondensation is additionally carried out to further increase the molecular weight.
In the process for preparing a polyester, an antimony compound, a germanium compound or the like has been hitherto used as a polycondensation catalyst.
However, polyethylene terephthalate prepared by the use of the antimony compound as a catalyst is inferior to polyethylene terephthalate prepared by the use of a germanium compound as a catalyst in transparency and heat resistance, so that improvement of the transparency and heat resistance in the former process has been desired. For the use of the antimony compound as a polycondensation catalyst, it has been also desired to reduce the acetaldehyde content in the resulting polyester.
In the use of the germanium compound, there resides a problem that the cost for the polyester production is high because the germanium compound is considerably expensive. On this account, a process of collecting and recycling the germanium compound scattered during the polycondensation has been studied to reduce the production cost.
It is known that titanium is an element having a function of accelerating polycondensation reaction of an ester low polymer, and titanium alkoxide, titanium tetrachloride, titanyl oxalate, orthotitanic acid and the like are publicly known as polycondensation catalysts. In order to use such titanium compounds as the polycondensation catalysts, many studies have been made.
For example, a slurry catalyst for polyester preparation in which a hydrolyzate of titanium tetrachloride is dispersed in an alcohol such as butanol is disclosed in U.S. Pat. No. 3,463,742.
The conventional titanium compound catalyst, when used as the polycondensation catalyst, however, is inferior to the antimony compound or the germanium compound in activity. The resulting polyester has a problem of being markedly colored yellow, so that its practical use has not been realized yet. In the industrial production of polyesters, a catalyst containing a large amount of chlorine, such as titanium tetrachloride or a partial hydrolyzate thereof causes a problem of corrosiveness associated with elution of a chlorine component, and hence a catalyst containing smaller amount of a chlorine component has been desired.
Under such circumstances as described above, the present inventors have earnestly studied polycondensation catalysts for use in the polyester preparation, and they have found that a polyester of high quality can be prepared with high catalytic activity by using, as a polycondensation catalyst, a titanium compound which is prepared by dehydro-drying a hydrolyzate obtained from a specific titanium compound.
The present inventors have further studied and, as a result, they have found that if a solid titanium compound obtained by contacting the hydrolyzate with a specific alcohol and then dehydro-drying the contact product in the above-mentioned catalyst preparation process, is used as a polycondensation catalyst, a polyester of high quality can be prepared with high catalytic activity. They have also found that if a titanium-containing solution in which the above-mentioned contact product of the hydrolyzate with the specific alcohol is dissolved in ethylene glycol, is used as a polycondensation catalyst, a polyester of high quality can be prepared with high catalytic activity. Based on the findings, the present invention has been accomplished.
That is to say, it is an object of the present invention to provide a catalyst for polyester preparation capable of preparing a polyester of excellent quality with excellent catalytic activity and a process for preparing a polyester using the catalyst. It is another object of the invention to provide a polyester of excellent transparency, hue, etc. obtained by the use of the catalyst.
The first catalyst for polyester preparation according to the invention comprises a solid titanium compound containing titanium, oxygen, carbon and hydrogen and having a Tixe2x80x94O bond, and has a maximum solubility in ethylene glycol, as measured under heating at 150xc2x0 C., of not less than 3,000 ppm in terms of a titanium atom.
The weight ratio (Ti/C) of the titanium atom to the carbon atom in the solid titanium compound is preferably in the range of 50 to 1.
The maximum solubility of the solid titanium compound in ethylene glycol is preferably in the range of 3,000 to 5,000 ppm in terms of a titanium atom.
The solid titanium compound preferably has an average particle diameter of 1 to 30 xcexcm.
The solid titanium compound may further contain at least one element selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc, boron, aluminum, gallium, silicon, germanium, tin, antimony and phosphorus (these elements are also referred to as xe2x80x9cother elementsxe2x80x9d hereinafter).
The solid titanium compounds referred to in this specification include solid titanium compounds containing other elements unless otherwise stated.
The solid titanium compound is a contact product of a hydrolyzate of a titanium halide or a hydrolyzate of a titanium alkoxide with a polyhydric alcohol, or a contact product of a hydrolyzate of a mixture of a titanium halide or a titanium alkoxide and a compound (also referred to as a xe2x80x9ccompound of other elementxe2x80x9d hereinafter) of at least one element selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc, boron, aluminum, gallium, silicon, germanium, tin, antimony and phosphorus, with a polyhydric alcohol.
The polyhydric alcohol is preferably ethylene glycol or glycerol.
The solid titanium compound can be obtained by, for example, drying the contact product of the hydrolyzate with the polyhydric alcohol by means of a granulation dryer.
Another embodiment of the first catalyst for polyester preparation according to the invention comprises:
(I-a) the solid titanium compound, and
(II) a compound of at least one element selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, boron, aluminum, gallium, manganese, cobalt, zinc, germanium, antimony and phosphorus.
The second catalyst for polyester preparation according to the invention comprises a titanium-containing solution in which a contact product of a hydrolyzate of a titanium halide or a hydrolyzate of a titanium alkoxide with a polyhydric alcohol is dissolved in an ethylene glycol-containing solution in an amount of 3,000 to 100,000 ppm in terms of a titanium atom.
Another embodiment of the second catalyst for polyester preparation according to the invention comprises a titanium-containing solution in which a contact product of a hydrolyzate of a mixture of a titanium halide or a titanium alkoxide and a compound of other element, with a polyhydric alcohol is dissolved in ethylene glycol in an amount of not less than 3,000 ppm in term of a titanium atom.
The titanium-containing solution preferably has a haze of not more than 20%.
The titanium-containing solution preferably has a moisture content of 0.05 to 2.0% by weight.
The titanium-containing solution may contain a solubilizing agent, and the solubilizing agent is preferably contained in an amount of 1 to 50% by weight based on the ethylene glycol-containing solution.
The solubilizing agent is preferably glycerol or trimethylolpropane.
The titanium-containing solution may contain an acid component, and the acid component is preferably contained in an amount of 1 to 20% by weight based on the ethylene glycol-containing solution.
The acid component is preferably sulfuric acid or an organic sulfonic acid.
The ethylene glycol-containing solution may be one composed of only ethylene glycol or may be one containing a solubilizing agent, an acid component, etc., in addition to ethylene glycol.
A further embodiment of the second catalyst for polyester preparation according to the invention comprises:
(I-b) the titanium-containing solution, and
(II) a compound of at least one element selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, boron, aluminum, gallium, manganese, cobalt, zinc, germanium, antimony and phosphorus.
The process for preparing a polyester according to the invention comprises polycondensing a dicarboxylic acid or its ester-forming derivative with a diol or its ester-forming derivative in the presence of the first or the second catalyst for polyester preparation to produce a polyester.
The polyester prepared by the process for preparing a polyester according to the invention is preferably an aromatic polyester and is particularly preferably polyethylene terephthalate.
The polyester according to the invention is obtained by the above process for preparing a polyester.
The polyester according to the invention is preferably an aromatic polyester and is particularly preferably polyethylene terephthalate.
When the polyester according to the invention is polyethylene terephthalate, the titanium content is preferably in the range of 1 to 100 ppm and the weight ratio (Mg/Ti) of the magnesium content to the titanium content is preferably not less than 0.01.